Conventionally, there has been known an accumulator fuel injection device where fuel that is pressure-fed from a high pressure pump is accumulated in a common rail that serves as a pressure accumulator and where fuel of an even pressure is distributed from this common rail with respect to plural fuel injection valves. FIG. 14 shows an example of this common rail, which is disposed with a rail body portion 312 and plural branching pipe portions 314 (in the example of FIG. 14, five) that are arrayed along an axial direction (X direction) of the rail body portion 312, are formed integrally with the rail body portion 312 and are disposed so as to project outward in a circumferential direction of the rail body portion 312. A flow path 318 is formed inside the rail body portion 312 along the axial direction, and branching paths 316 that branch from the flow path 318 are formed inside the branching pipe portions 314. Further, fuel pipes (not shown) are connected to the branching pipe portions 314, other end sides of the fuel pipes (not shown) that are connected to injection-use branching pipes 314a to 314d of the branching pipe portions 314 are connected to fuel injection valves (not shown), and the other end side of the fuel pipe (not shown) that is connected to an inflow-use branching pipe 314e is connected to a fuel supply-use pump (not shown).
In this common rail, internal pressure resulting from the high pressure fuel acts with respect to the inner surfaces of the flow path and the branching paths. Additionally, it is easy for stress to concentrate at intersecting portions where the branching paths branch from the flow path, and stress that is larger than at other portions acts thereon, so the risk that damage such as cracks will arise becomes higher when the common rail is part of a system that injects fuel of a higher pressure.
Thus, there has been proposed a common rail housing that can reduce the stress value of its stress concentration portions and significantly improve its pressure resistance. More specifically, as shown in FIG. 15, there has been disclosed a common rail housing that is configured such that the cross-sectional shape of pressure accumulating chambers 302 that pressure-accumulate high pressure fuel that has been supplied from the fuel supply-use pump is given an elliptical shape, whereby the pressure accumulating chambers 302 and second fuel passage holes 306 are disposed so as to intersect in an orthogonal direction at positions where the radius of curvature is larger than in the case of perfectly circular pipes that include pressure accumulating chambers whose cross-sectional shape is perfectly circular, whereby the stress value of intersecting portions (stress concentration portions) 309 can be reduced (e.g., see Patent Document 1).
[Patent Document 1] JP-A-2001-295723 (claims, FIG. 1)